1. Field of the Invention
The invention relates to a device for the automatic slack adjustment of a brake including a brake lever, disposed on a brake operating shaft, and furnished with a brake slack adjustment device between the brake lever and the brake operating shaft, where the slack adjustment device adjusts the brake operating shaft relative to the brake lever around the rotation axis of the brake operating shaft.
2. Brief Description of the Background of the Invention Including Prior Art
Such a device has been known from the PCT application publication WO No. 82/01922. The conventional device includes a slack adjustment device, which slack adjustment device allows to adjust the parts of the brake actuator relative to each other, namely a brake operating shaft and a brake lever disposed on the brake operating shaft. The adjustment serves for a continuous readjustment of the brake actuator, which is subject to a deviation from a preset starting position based on brake lining wear. The slack adjustment device can be actuated with a drive device when the brake lever is moved into brake operating direction. The drive device is disposed between a reference point, fixed relative to the brake lever, and the slack adjustment device. A gear coupling with an increased gear play serves as a lost motion device between the drive device and the slack adjustment device. The lost motion device allows a brake lever deflection without an actuation of the slack adjustment device. Transfer means of the drive device comprise a spur wheel pair and a worm drive connected to the spur wheel pair. These transfer means allow a generous assembly tolerance of the brake lever relative to the fixed reference point. Disadvantageous in this case is the relatively large construction expenditure for the transmission means as well as the requirement for an increased production expenditure for the bearing supports, disposed on rotary axes running staggered relative to each other.
A similar automatic brake adjustment device is known from the German Patent Application Laid Out DE-AS No. 1,480,038 where a gear rack drive is employed instead of the previously recited worm drive. The slack adjustment of the wear-caused release gap and brake slack play is performed by the motion of the brake lever in the brake release direction and not in the brake actuation direction as in the previously recited device. The drive force at the adjustment mechanism for the adjustment of the brake slack play during the brake cylinder release stroke in brake release direction can be obtained in this case only from the existing pull-back springs of the brake operating elements. In case of a relatively hard-operating brake actuator, frequently additional auxiliary pull-back springs have therefore to be disposed on the outside at the brake actuator in order that a still sufficient drive force remains available for the slack adjustment motion and for the release of the brake. The gear rack drive requires a stop fixedly disposed at the casing. The starting position of the gear rack drive is defined by the position of the stop. The device therefore requires in a disadvantageous manner a precise adjustment of the brake lever relative to the fixed reference point. The exceeding of a deviation tolerance can result in a breakage of the device after the gear rack drive reaches the stop fixedly disposed at the casing.
The German Patent DE-PS No. 3,625,107 teaches an automatic slack adjustment device for the expanding cam of a drum brake. The reference teaches to employ a worm 4 and a worm gear to provide an automatic slack adjustment device for vehicle brakes. A coupling part is supported with limited shiftability against the force of a compression spring on a worm shaft such that the gear 6 and 8 become disengaged (column 4, lines 29 through 32). The reference teaches a second coupling which is formed as a free wheel and which allows motions in an opposite rotary sense relative to a first coupling. The presence of two coupling parts makes this adjustment device relatively complicated.
The German Printed Patent document DE-OS No. 2,104,921 teaches a slack adjustment device for brakes. The reference teaches that a worm is rotatable upon release of a bolting relative to a lever and that a worm wheel can be rotated around an axis and thus the brake slack of the brake device can be adjusted. If an excessive brake slack is determined, then the brake slack can be automatically adjusted by rotation of the worm. It appears that the reference device allows only a slack adjustment and determination with a limited precision and reliability.
The German Printed Patent document DE-OS No. 2,528,603 teaches a device for the adjustment of the slack of a brake The reference teaches an automatic adjustment means, which is connected with an adjustment shaft 34 such that, upon rotation of a control lever 30 around a predetermined angle in the direction of brake actuation, the automatic adjustment means rotate the adjustment shaft in the direction of readjustment of the brake. The reference teaches that the grooves are wider than the width of the springs so that the drive shell 52 can be rotated relative to the adjustment shaft 34 by a preset value until the edges of the springs contact the corresponding edges of the grooves. The reference teaches a connection between the drive shell 52 and the adjustment shaft 34.
Thus, the art show various features which have been employed in connection with the construction of slack adjusters for brake systems.